Phyiologia (July 1994) 77(l):38-44. REVISIONARY STUDY OF LASIARRHENUM {BOR^Q\H^CE^E) Billie L. Turner Department of Botany, University of Texas, Austin, Texas 78713 U.S.A. ABSTRACT Lasiarrhenum, regarded by I.M. Johnston (1954) as monotypic, is treated as having three species: L. trinervium (Lehm.) B.L. Turner, comb. nov. [an earlier name for L. strigosum (H.B.K.) I.M. Johnst., the generitype]; L. pinetorum I.M. Johnst. (upon which Johnston erected the monotypic genus Perittoatema I.M. Johnst.); and L. confundum B.L. Turner, ap. nov.^ a localized endemic from southwestern Durango, Mexico. Since the latter species possesses characters which bridge the "morphological gap" between Laaiarrhenum and Perittoatema, I have reunited the two genera, much as Johnston originally treated these. Distributional maps, key to species, and cornplete synonymy are given for the taxa concerned. KEYWORDS: Boraginaceae, Lasiarrhenum, Perittostema, Mexico The genus Lasiarrhenum was erected as monotypic by Johnston in 1924, and maintained by him in his subsequent account of the Mexican borages (Johnston 1954). Since he rendered an excellent description of the single species involved, such is not repeated here, but I have emended the generic de-scription of Laaiarrhenum to include L. pirietorum (which Johnston described in 1935 but subsequently created for this the monotypic genus Perittostema) and L. confundum, described herein. Johnston (1954) summarized his views on relationships among genera of the tribe Lithospermae for North America. In this, Lasiarrhenum and Perit-tostema were positioned near the genera Lithospermum, Macromeria, and Onosm,odium. My taxonomic interest in the latter two genera prompted the present study. 38
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